fix: make image processing work in github copilot provider

[alexhancock]

Fixes #5497 by sending the Copilot-Vision-Request header with a value of true when there is a processed image in the message

Working example after the change:

[Copilot]

Pull Request Overview

This PR fixes image processing in the GitHub Copilot provider by adding the Copilot-Vision-Request header when images are detected in the request payload.

• Introduces payload_contains_image() helper function to detect images in message content
• Modifies get_github_headers() to accept optional payload and conditionally add the vision header
• Updates all call sites to pass None when payload inspection is not needed

Reviewed Changes

Copilot reviewed 1 out of 2 changed files in this pull request and generated no comments.

File	Description
crates/goose/src/providers/githubcopilot.rs	Added image detection logic and updated header generation to include Copilot-Vision-Request header when images are present in the payload
ui/desktop/openapi.json	Added newline at end of file for proper formatting

[DOsinga]

you could do this more functional, like messages.iter.any and then cast the is_object to a single list but up to you

[DOsinga]

I'd drop this comment, but do what it says :)

adding payload to get_github_headers seems a tad awkward. if you just break up that builder below you just go:

let mut request = self.client.post(..).headers()
if has_images:
  request = request.header(that_header)
response = request.header(..).send.await?

or some such

then you can leave the other bits alone